More than 10,000 runners took to the streets of Pittsburgh this May for the return of the Pittsburgh Marathon. The revamped race (back from a five-year hiatus) was designed to reflect all the changes the city has seen in recent years — it wove through vitalized parks, showcased new industries and above all vowed to green up its image. The marathon joined what has become a nationwide trend in mass-participation sporting events and swore to get its act together.

Anyone who's run a 5K or triathlon is familiar with their ugly side. The roads are papered with waxy Dixie cups from water stations. Trash cans overflow with plastic wrappers from end-of-race snacks. Abandoned goodie bags sit unclaimed near the staging areas.

And that's just the harm we can see. People don't often think about the carbon footprint of a race that draws spectators and participants from around the globe. Big marathons like Boston's or New York's draw runners from many continents, most of them traveling by airplane or car. According to CarbonCounter, more than 1,700 competitors traveled 18.3 million miles to reach the 2007 Ironman Hawaii, generating an average of 1.3 pounds of carbon dioxide per passenger mile. And that was only about 10 percent of the runners in a typical continental marathon. Needless to say, these events generate as much waste as they do sweat.

"In the days of the ancient Greeks and the original Olympics, people just showed up and ran — naked!" Henderson says. "It was a more pure form of the sport, and we seem to have gotten away from that."

Henderson points to enormous competition among races to be the event of the season, shifting many of their priorities from the "quality and safety of the race" to entertainment and the "massive goodie bags."

When he planned the 2007 Portland Triathlon, Henderson wanted things to be different. He advertised the race as green and sustainable from the get-go, finding that an emphasis on these qualities fostered more awareness in the participants.

"For example, we had no litter at the transition area," he says. "None. There was this collective consciousness ... where people thought, 'Hey, this race is trying to be responsible, so let's do that, too.'"

Henderson realized he could help other races make the same changes by setting out some guidelines. In 2008, the Council for Responsible Sport — aka ReSport — was born.

Today, dozens of races are applying for ReSport certification levels, ranging from "Evergreen" (like the Marin County Triathlon) to "Certified" (like the 2009 Austin Marathon). Henderson and his team developed categories of responsibility like recycling/composting waste, emphasizing local participation and community sourcing, offsetting carbon emissions, using alternate fuels for race vehicles and generators, using electronic communication with participants, and giving serious, sustainable thought to medals and goodie bags.

Henderson says the process for certification can take as little as three weeks, and ReSport keeps costs and paperwork low. "[Certification] is not meant to be an extra step ... we worked hard to make it simple and straightforward so events can see how it makes sense to [make these changes]."

Because some of these "Evergreen" innovations can be more costly, ReSport recommends solutions like higher race fees (with explanations) or suggesting additional fees for emissions offsets — and many races find that athletes support their emphasis on sustainability.

Boasting a ReSport certification (or green race ideals) means something to many of today's athletes. While it didn't seek certification from ReSport, the Pittsburgh Marathon met a lot of the goals: Race directors composted fruit from the finish area, used compostable cups at water stations and used 100 percent electronic communication (spectators could even get text messages with updates on their favorite runners).

Henderson hopes this trend continues. "We really want athletes to be selective when they attend events and 'vote' with their registrations," he says. "That will provide further incentive for event directors to do good things." He's quick to point out that, as athletes, we have responsibilities, too. "We don't want people to stop traveling or stop participating in sports. But we do want people to see what impact they are having."

Selecting only one destination race per season and supporting local races can make a huge difference, as can carpooling or taking public transportation to staging areas. And wherever you're running, you can make your voice heard by contacting race organizers to make sure they're aware of all the sustainable steps they can take.